JBMS STUDY GUIDE FOR REFRACTION QUIZ

1. Light travels in a straight line. What is the evidence for this?

You cannot see around a corner! You only see something when the light that bounces off an object reaches your eye. You must be in the direct line of sight in order for them to reach your eye. https://www.youtube.com/watch?v=2nwK78F_4eA for more information.

2. When do light rays bend? What is the evidence for this?

Light rays bend when they change medium and hit at an angle. When we did the demonstration in class, the line of students changed direction when they entered the “slower” medium. Please see http://www.physicsclassroom.com/class/refrn/Lesson-1/The-Cause-of-Refraction if you want further clarification.

Other evidence of light rays bending was the appearance of a pencil or ruler placed in a glass beaker of water.

The part of the pencil in the water: When light reflected from the pencil reached your eye it traveled through the water and when it reached the curved surface of the glass, it changed direction when it changed medium – because the glass was curved, the light rays did not bend equally and therefore the image appeared magnified. The light rays reached your eye in a slightly different position.

The part of the pencil in the air: The light did not change medium, but traveled in air the whole time. The light rays stayed in the same relationship to each other and the image your eye perceived was not magnified.

When you looked at the pencil in the water, it appeared to be “broken” at the water line. This was because only part of the image of the pencil was magnified.

We looked through a  triangular glass prism and saw that the laser beam was bent and did not travel in a straight line. We also saw that the prism refracted sunlight into a “rainbow” of colors.

3. A lens makes light rays focus at one point. This is called a focal point. What is the evidence for this?

When you looked through the magnifying glass you were able to focus the sun’s light to a single point. Some people used a flashlight to get the same effect.

When we projected the image of the window onto a piece of paper, there was one particular distance when the image was clear and upside down. This distance was the focal distance of the lens.

We saw that the differently curved lenses had different focal points.

4. A shadow happens when light rays are blocked.

This is evidence that light travels in a straight line. https://www.youtube.com/watch?v=2nwK78F_4eA provides more information.

5. You only see light when it is reflected into your eyeball.

Light can be there but we cannot see it unless it strikes something and gets reflected into the eye. A laser beam can only be seen when it strikes a surface such as a floor or the wall. However, when we placed a piece of paper in the air in front of the path of the laser light, the light reflected off the paper and traveled to our eye, so we could see it.

6. Convex lenses curve out. These are the kinds of lenses that magnify.

We saw that the magnifying glasses used convex lenses.

7. Why do objects appear black?

Black objects absorb all the light that reaches them. No light rays are reflected back to your eye.

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